A DFT study of superior adsorbate–surface bonding at Pt-WSe2 vertically aligned heterostructures upon NO2, SO2, CO2, and H2 interactions

This study investigates the potential of platinum (Pt) decorated single-layer WSe2 (Pt-WSe2) monolayers as high-performance gas sensors for NO2, CO2, SO2, and H2 using first-principles calculations. We quantify the impact of Pt placement (basal plane vs. vertical edge) on WSe2’s electronic properties, focusing on changes in bandgap (ΔEg). Pt decoration significantly alters the bandgap, with vertical edge sites (TV-WSe2) exhibiting a drastic reduction (0.062 eV) compared to pristine WSe2 and basal plane decorated structures (TBH: 0.720 eV, TBM: 1.237 eV). This substantial ΔEg reduction in TV-WSe2 suggests a potential enhancement in sensor response. Furthermore, TV-WSe2 displays the strongest binding capacity for all target gases due to a Pt-induced “spillover effect” that elongates adsorbed molecules. Specifically, TV-WSe2 exhibits adsorption energies of − 0.5243 eV (NO2), − 0.5777 eV (CO2), − 0.8391 eV (SO2), and − 0.1261 eV (H2), indicating its enhanced sensitivity. Notably, H2 adsorption on TV-WSe2 shows the highest conductivity modulation, suggesting exceptional H2 sensing capabilities. These findings demonstrate that Pt decoration, particularly along WSe2 vertical edges, significantly enhances gas sensing performance. This paves the way for Pt-WSe2 monolayers as highly selective and sensitive gas sensors for various applications, including environmental monitoring, leak detection, and breath analysis.

swift and precise responses 23,24 .Its larger surface area and chemical stability contribute to improved adsorption and durability, while low noise levels and selective customization enhance accuracy.WSe 2 's compatibility with microfabrication enables compact devices and effective room-temperature operation.Ongoing research, exemplified by Guo et al. 25 , showcases WSe 2 nanosheets with high sensitivity to NO 2 at room temperature, high selectivity, and stability for 8 weeks.Similarly, Wu et al. 26 demonstrate a WSe 2 monolayer-based NO 2 gas sensor with detection capabilities across varying concentrations and temperatures, emphasizing rapid recovery, high selectivity, reversibility, and stability over 60 days for NO 2 detection.
The use of 2D materials, especially TMDs like WSe 2 , in gas sensors is gaining attention for their superior performance attributed to a high surface-to-volume ratio 27 .Monolayers of WSe 2 , a significant member of dichalcogenides, exhibit remarkable electronic properties and substantial surface area, enhancing the sensitivity and range of gas sensors with specific doping or surface modifications.This is crucial for devices detecting harmful gases (NO 2 , HCHO, NH 3 , SF 6 decomposed gases) in residential and occupational environments 28 .Noble metaldecorated WSe 2 is recognized as a promising material for gas sensing applications.Pt atoms are a frequent choice for absorbing molecules on TMDs due to several key properties.Pt's well-known catalytic activity aids in weakening bonds and facilitating desired chemical reactions on the TMD surface.It can also modify the TMD's work function, influencing the adsorption and release of specific gas molecules for targeted sensing or manipulation.Additionally, Pt offers good thermal and chemical stability, making it practical for applications where the TMD-Pt composite might encounter harsh environments.Compared to generic metal decoration, Pt provides a more targeted approach due to its specific catalytic properties and work function effects.Furthermore, Pt can influence the TMD's electronic structure at the interface, potentially enhancing its conductivity.The combination of Pt and the TMD can even create synergistic effects, leading to superior performance compared to either material alone.Density Functional Theory (DFT) computations play a crucial role in examining gas sensing and functionalization of single-atom catalysts, revealing improved sensitivity of Pd-functionalized WSe 2 systems in detecting harmful gases.Doping WSe 2 with noble metals (Pd, Ag, Au, Pt) enhances gas sensing, with Ag-WSe 2 showing potential for efficient NO 2 sensing 29 .Noble metal catalysts like Pt/Pd are proposed to boost H 2 gas sensor sensitivity at room temperature.Studies indicate that Pd film on TiO 2 enhances H 2 sensitivity 30 , while Pt nanoparticles in F-MWCNT/TiO 2 /Pt hybrid achieve notable sensitivity to H 2 molecules at specific concentrations 31 .
Comprehending the importance of further theoretical and experimental exploration in understanding and optimizing the gas sensing capabilities of single-atom Pt-decorated WSe 2 (Pt-WSe 2 ).While significant progress has been made in comprehending the effects of single-atom doping, especially in materials like molybdenum disulfide (MoS 2 ), there remains a notable gap in theoretical inquiries regarding the adsorption phenomena of representative gases (H 2 , NO 2 , CO 2 , and SO 2 ) on monolayers of Pt-WSe 2 .The research aims to address this gap by investigating the interactions between these target gas molecules and WSe 2 layers coated with single-atom Pt, providing valuable insights for gas sensing applications.Consequently, this methodology integrates the distinctive characteristics of WSe 2 , including its elevated surface-to-volume ratio and semiconducting nature, with the catalytic attributes of Pt, leading to an enhanced gas sensing platform with improved efficiency.Gas sensing has advanced significantly as a result of the combination of these materials and methods.
This study employs DFT to investigate the gas sensing capabilities of a Pt-WSe 2 -based system toward specific target gases (H 2 , NO 2 , CO 2 , and SO 2 ).Pt-atom is strategically decorated over the basal and vertical edges of the WSe 2 monolayer.The analysis encompasses electronic characteristics, including band structure, density of states (DOS), charge density difference (CDD), and population analysis for different gases.The vertical configuration of Pt-WSe 2 demonstrates outstanding sensitivity and recovery time for H 2 , attributed to the spillover effect.The findings propose a promising strategy to enhance the sensing response to hydrogen gas, elucidating the impact of Pt functionalization on the sensing mechanism.

Computational methods
This paper employs the Dmol 3 package in Material Studio software for all theoretical and DFT calculations 32,33 .The Perdew-Burke-Ernzerhof (GGA-PBE) generalized approximation is utilized to handle electron exchange correlation accurately 34,35 .The study incorporates Density Functional Theory with dispersion (DFT-D) and van der Waals (vdWs) interactions to enhance accuracy, addressing the traditional DFT's challenges in capturing weak forces 36,37 .Tkatchenko and Scheffler's (TS) method is applied for precise simulation of vdWs interactions 38,39 .DFT semi-core pseudopotentials (DSPP) replace core electrons of specific atoms, enhancing accuracy in electronic interaction descriptions 40 .DSPP, combined with Double numerical plus polarization (DNP) basis sets, is used to describe electronic wavefunctions, improving predictions of molecular properties and behaviour.The approach involves two sets of functions for core and valence electrons, including extra functions for electron density changes due to neighbouring atoms (polarization).This comprehensive methodology enhances accuracy in describing electronic interactions and predictions of molecular behaviour.In geometry optimizations, the criteria for energy convergence, maximum force, and maximum displacement were set at 1.0 × 10 -5 Ha, 0.002 Ha/Å, and 0.005 Å, respectively.A global orbital cutoff radius of 5.0 Angstroms was used.For calculating DOS, a 7 × 7 × 1 Monkhorst-Pack k-point grid was employed, while a 3 × 3 × 1 Monkhorst-Pack k-point grid was utilized for other calculations, ensuring an accurate representation of the Brillouin zone 41 .The WSe 2 structure was cleaved along the [1 0 0] direction to expose the vertical edge.Moreover, for the analysis, we have considered a 3 × 3 × 1 WSe 2 supercell with a vacuum region of c = 15 Å in order to avoid contact with surrounding WSe 2 layers.Furthermore, the study involves calculating adsorption energy (E ad ) using Eq.(1), respectively.The CDD for the adsorption configuration (Δρ) is determined using Eq. ( 2).(Refer to Eqs. (1), (2) in the supporting information).Moreover, in physisorption, the dominant interactions between the adsorbate and adsorbent are typically weak, characterized by van der Waals forces or dipole-dipole interactions.This is reflected in the observation that the sum of covalent radii tends to exceed the adsorption distance.Conversely, chemisorption involves stronger www.nature.com/scientificreports/interactions, often leading to the formation of chemical bonds between the adsorbate and adsorbent surface.Here, the adsorption distance closely aligns with the sum of covalent radii, indicating the potential for chemical bond formation.This interpretation is substantiated by previous studies utilizing density functional theory (DFT) calculations, which have consistently demonstrated this correlation 42,43 .

Results and discussion
To examine the gas sensing behaviour of WSe 2 , firstly we examine the physical and electrical properties of individual monolayer structures of WSe 2 as shown in Fig. 1a, focusing on its geometric structure.The available chalcogen vacancies play a significant role in the electronic configuration of TMDs 44 .Subsequently, we investigate the properties of Pt-coated WSe 2 .In this study, we specifically consider WSe 2 with a monolayer structure, where cutting the (001) plane results in the formation of hexagonal lattices with a honeycomb-like arrangement.Following structural optimization, the monolayers of WSe 2 displayed a bond length of 2.555 Å between W and Se atoms, and a bond length of 3.380 Å between the Se atoms (Fig. 1b).The calculated outcomes and the reported values of 2.54 Å (W-Se) exhibited a notable concordance, indicating a satisfactory agreement between them 45 .Moreover, in Fig. 1c we showed the bandgap for the WSe 2 monolayer which shows the value of 1.576 eV between the conduction and valence band representing good agreement with previously reported work 46 .Figure 1d presents the projected density of states (PDOS) for the pristine WSe 2 monolayer.The PDOS reveals significant hybridization between the W 4d orbitals and the Se 4s and 4p orbitals, indicating the formation of covalent bonds between the W and Se atoms.
This study employs computational simulations to investigate the impact of Pt decoration on the electronic properties of a WSe 2 monolayer.Moreover, we considered three potential sites for decoration and they are labelled as T BH-WSe2 (Pt-atom decorated over the hallow hexagonal site in WSe 2 basal plane configuration), T BM-WSe2 (Pt-atom decorated over the W atom in WSe 2 basal plane configuration), and T V-WSe2 (Pt-atom decorated at the vertical edge of WSe 2 ) as illustrated in Fig. 2a-c.
Furthermore, the optimized configurations of T BH-WSe2 , T BM-WSe2 , and T V-WSe2 reveal bandgap and DOS values of 0.720 eV, 1.237 eV, and 0.062 eV, respectively (Figs.S1-S3).We have analyzed the electronic spin for Pt-WSe 2 (Fig. S11(a1-a3) in Supplementary Information for details).Pt functionalization on the WSe 2 monolayer induces the hybridization of electronic orbitals, creating new states within the bandgap and reducing bandgap values.The Pt placement significantly influences the electronic properties of WSe 2 , highlighting potential functionality tailoring.Adsorption energy is negative, indicating an exothermic process.Bond lengths vary slightly post-optimization, with bond lengths between Pt-atom and W-atom for T BH-WSe2 and T V-WSe2 at 3.917 Å and 2.802 Å, respectively, and Pt and Se atom bond lengths in T BM-WSe2 at 2.429 Å. Mulliken and Hirshfeld , respectively (Fig. S4).Previous studies suggest that Pt-atom promotes catalytic oxidation, leading to hole accumulation layers.Rosy and green colours in Fig. S4 represent electron depletion and accumulation, respectively.The thermodynamic stability of T BH-WSe2 , T BM-WSe2 , and T V-WSe2 combinations was evaluated by molecular dynamics (MD) simulations performed at 500 K to examine their thermal stability.Moreover, phonon dispersion simulations were conducted to analyze the vibrational modes of T V-WSe2 , as shown in Fig. S5.Additionally, the optimized arrangement of target gases is depicted in Fig. S6.

H 2 adsorption
Figure 3 depicts the stable adsorption and CDD of the H 2 gas molecule for all three proposed structures namely T BH-WSe2 (Fig. 3a), T BM-WSe2 (Fig. 3b), and T V-WSe2 (Fig. 3c).It can be observed that there is elongation in the H-H bond (~ 0.212 Å) which denotes the dissociation of the H 2 molecule and supports the spillover effect 47 due to the decoration of Pt.The enhanced H 2 detection capabilities of Pt-WSe 2 arise primarily from two contributing factors: the presence of Pt-atom and the interfacial contact between Pt and WSe 2 .Pt-atom acts as a potential candidate for efficient H 2 sensing, facilitating the "spillover effect" where captured H 2 molecules migrate to the WSe 2 surface for subsequent adsorption.Moreover, the contact between Pt and WSe 2 promotes the generation of new adsorption sites on the WSe 2 monolayer, further enhancing the overall H 2 binding capacity.Therefore, both the Pt-atom and the synergistic Pt-WSe 2 interface play crucial roles in the superior H 2 detection performance of Pt-WSe 2 .In the Pt-WSe 2 system, upon interaction with H 2 gas molecules, an initial adhesion occurs between the catalytic Pt-atom and the gas molecules, leading to subsequent dissociation into single hydrogen atoms.This establishes the conditions necessary for a chemical interaction to occur between H atoms and the WSe 2 material, hence promoting the process of H atom diffusion into the WSe 2 structure.This causes chemisorption among all three proposed configurations.Moreover, a reduction in electrical resistance when H 2 comes in contact with the Pt-WSe 2 sensor.The observed decrease in resistance implies that H 2 tends to transfer electrons to the WSe 2 material.In other words, H 2 is a reducing nature gas due to which it will donate electrons to the system which is confirmed with the help of Mulliken and Hirshfeld's analysis and the gap between Pt and H atom shown in Table 1.www.nature.com/scientificreports/Consequently, it can be observed from Table 1 total charge over the H 2 molecule is positive which displays the depletion of electrons.And these electrons are transmitted to the Pt-atom which possesses a negative value which is also illustrated in the CDD diagram.Furthermore, we have provided the electronic structure analysis (i.e., band structure, DOS, and PDOS) after the adsorption of the H 2 gas molecule in the supplementary information (Fig. S7).We investigated the electronic spin response upon H 2 adsorption (Fig. S11(b1-b3); refer to Supplementary Information for details).In addition, we have calculated the adsorption energies for the T BH-WSe2 , T BM-WSe2 , and T V-WSe2 configurations towards the H 2 gas molecule and obtained the values of − 0.0293 eV, − 0.0788 eV, and − 0.1261 eV, respectively.It could be easily seen that the most favourable case for strong H 2 adsorption was exhibited by T V-WSe2 .

NO 2 adsorption
The Fig. 4 illustrates the stable adsorption and CDD of the NO 2 gas molecule on three suggested structures: T BH-WSe2 (Fig. 4a), T BM-WSe2 (Fig. 4b), and T V-WSe2 (Fig. 4c).Notably, there is an elongation observed in the N-O bond, approximately to 0.060 Å, indicating the weak interaction between the Pt-atom and the NO 2 molecule.Furthermore, this minor extension in bond is corroborated by the low binding capacity arising from the Pt decoration.
The Pt-N minimum adsorption distance, measuring 2.367 Å, surpasses the sum of relevant covalent radii (2.010 Å for Pt-N 48 ), indicating a physisorption nature.It is evident that physisorption was consistently observed for NO 2 in all three suggested arrangements.Additionally, it is essential to note that NO 2 gas exhibits an oxidizing nature, causing it to withdraw electrons from the system.This aspect has been confirmed through the comprehensive analysis performed using Mulliken and Hirshfeld's population analysis method, and the findings are presented in Table 2 with the adsorption length between Pt and O atom.
As a result, Table 2 reveals that the total charge on the NO 2 molecule is negative, signifying the accumulation of electrons within the molecule.These electrons are then extracted from the Pt-atom, which, as shown in the CDD diagram, possesses a negative value.Additionally, electronic structure analysis, including band structure, DOS, and PDOS after NO 2 gas molecule adsorption, is available in the supplementary information (Fig. S8).To understand the interaction between the material and NO 2 on a deeper level, we analyzed the electronic spin after gas adsorption as shown in Fig. S11(c1-c3) (see Supplementary Information for details).Additionally, we have conducted calculations for the adsorption energy of the T BH-WSe2 , T BM-WSe2 , and T V-WSe2 configurations upon exposure to NO 2 gas molecules.The obtained values are − 0.4227 eV, − 0.3879 eV, and − 0.5243 eV, respectively.Notably, the most favourable scenario for moderate adsorption is observed in the case of T V-WSe2 , signifying enhanced physisorption.The stronger adsorption energy of the T V-WSe2 system among all the proposed structures confirms more available W sites which enhance the adsorption towards the NO 2 gas molecule 49 .Overall, in this case, the Pt-atom facilitates the weak vdW interaction force for the NO 2 gas molecule.In Fig. 5, we can observe the stable adsorption and dissociation of the CO 2 gas molecule on three suggested structures: T BH-WSe2 (Fig. 5a), T BM-WSe2 (Fig. 5b), and T V-WSe2 (Fig. 5c).Significantly, the C-O bond exhibits an alteration of approximately 0.074 Å, indicating a weak vdW interaction between CO 2 and Pt.Additionally, noticeable deformations are observed in the CO 2 structure when it interacts with T BH-WSe2 and T BM-WSe2 .This deformation is a result of an enhanced adsorption energy (~ − 0.50 eV) and less adsorption distance in comparison to the T V-WSe2 -based configuration.In T BH-WSe2 and T BM-WSe2 , the Pt-atom interacts with the C atom, exhibiting adsorption distances of 2.012 Å and 2.138 Å, respectively.For T BH-WSe2 and T BM-WSe2 the adsorption distance is below and above the sum of relevant covalent radii (2.050 Å for Pt and C 48 ), indicative of chemisorption and physisorption, respectively.Conversely, in T V-WSe2 , the Pt-atom interacts with the O atom, with an adsorption distance of 3.416 Å exceeding the sum of relevant covalent radii (2.020 Å for Pt and O 48 ), suggesting a physisorption mechanism.These findings, supported by the CDD diagram (Fig. 5), elucidate distinct adsorption behaviours in the investigated Pt-WSe 2 variants.Consequently, based on these observations, it can be concluded that chemisorption takes place in the case of T BH-WSe2 , while physisorption occurs in the case of T BM-WSe2 and T V-WSe2 structures.Moreover, it is crucial to highlight that the CO 2 gas demonstrates an oxidizing characteristic, thereby extracting electrons from the system.To confirm this aspect, we conducted a comprehensive analysis using Mulliken and Hirshfeld's population analysis method, and the adsorption length is tabulated in Table 3. Table 3 presents intriguing findings, indicating a negative total charge on the CO 2 molecule, suggesting an accumulation of electron density over the CO 2 molecule.These electrons appear to be extracted from the Pt-atom, as evidenced by the negative value displayed in the CDD diagram.The impact of CO 2 adsorption on the electronic structure (band structure, DOS, and PDOS) and electronic spin is presented in the supplementary information (Figs.S9, S11(d1-d3)).Furthermore, we performed calculations for the adsorption energies of the CO 2 gas molecule on T BH-WSe2 , T BM-WSe2 , and T V-WSe2 configurations, resulting in values of − 0.5577 eV, − 0.5373 eV, and − 0.5777 eV, respectively.As it can be observed that there is slight deformation in the CO 2 configuration after the optimization (for T BH-WSe2 and T BM-WSe2 ), due to the stronger adsorption energy and less adsorption distance.

SO 2 adsorption
The adsorption configuration of the SO 2 gas molecule is similar to the CO 2 and NO 2 gas molecules for the T BH-WSe2 , T BM-WSe2 , and T V-WSe2 as shown in Fig. 6a-c.In addition, there is a variation in S-O bond length (~ 0.036 Å) after adsorption as it can be seen in the CDD diagram.This variation is due to the stronger adsorption energy of these structures as aforementioned.Consequently, it implies that there is weak vdW interaction exhibited between Pt-atom and SO 2 molecule.In T BM-WSe2 , the Pt-atom interacts with the S atom, with an adsorption  distance of 2.608 Å, exceeding the sum of relevant covalent radii (2.410 Å for Pt and S 48 ).Conversely, in T BH-WSe2 and T V-WSe2 , the Pt-atom interacts with the O atom, exhibiting adsorption distances of 2.355 Å and 2.320 Å, respectively, surpassing the sum of relevant covalent radii (2.020 Å for Pt and O 48 ).The consistent observation across all three configurations reveals that the adsorption distances are greater than the sum of relevant covalent radii, indicating a physisorption mechanism, as corroborated by the CDD diagram (Fig. 6).Additionally, it is essential to emphasize that SO 2 gas exhibits an oxidizing nature, resulting in the withdrawal of electrons from the system.To validate this phenomenon, we conducted an extensive analysis using Mulliken and Hirshfeld's population analysis method, and the adsorption length data are presented in Table 4.
The findings from Table 4 revealed a negative total charge on the SO 2 molecule, which implies the electron accumulation within the SO 2 molecule.These electrons seem to be drawn from the Pt-atom, as evidenced by the negative value shown in the CDD diagram.Further details regarding the electronic structure analysis (including band structure, DOS, and PDOS) and electronic spin upon SO 2 gas molecule adsorption can be found in the supplementary information (Figs.S10, S11(e1-e3)).Moreover, we obtained the adsorption energy of SO 2 gas molecules to be − 0.6813 eV, − 0.7511 eV, and − 0.8391 eV for T BH-WSe2 , T BM-WSe2 , and T V-WSe2 , respectively.The most promising results of T V-WSe2 , which suggests a potent physisorption action, are particularly remarkable.

Sensing mechanism
To interpret the sensing mechanism of Pt-WSe 2 composites, we examined the molecular interaction and charge transfer at the interface.It can be observed that the adsorption energy (as mentioned in Table S1) is improved in T V-WSe2 configuration among all proposed structures indicating strong interaction between the target gas molecule and Pt.A negative adsorption energy value signifies that the adsorption process releases heat, making it exothermic.Moreover, the adsorption energy (Fig. 7a) value is also listed in Table S1.(Refer to Table S1 in the supporting information).Moreover, to confirm the response of H 2 due to higher binding capacity we have calculated the sensitivity.The electrical conductivity ( σ ) can be defined as 50 : Here, e and µ represent carrier charge and mobility (constant because of monolayer), respectively.And n denotes the carrier concentration and it is defined as 50 : where E g represents the bandgap of the system.It can be seen that carrier concentration is dependent on the E g .The sensitivity (S) is defined as a relative change in resistance 51 : Using Eq. ( 3), the sensitivity can also be represented as: Equation (4) shows the simplified equation of S where, E g (Sys,Gas) , and E g (Sys,Isolated) represents the energy band gap of the system with and without gas adsorption, respectively.According to Eq. ( 4), the sensitivity value for distinct target gas molecules (H 2 , NO 2 , CO 2 , and SO 2 ) adsorbed T BH-WSe2 , T BM-WSe2 , and T V-WSe2 systems is tabulated in Table 5.
Figure 7b-f represents the schematic of energy band structure and gas sensing mechanisms for T V-WSe2 -based configuration towards NO 2 , CO 2 , SO 2 , and H 2 gas molecule.As we can see from the energy band diagram when a Pt single atom functionalized over WSe 2 , there is a difference between the Fermi level of WSe 2 and Pt i.e., work function (ϕ) of WSe 2 is less than Pt due to which the electrons will transfer from WSe 2 to Pt-atom until the Fermi levels of both the constituents (Pt and WSe 2 ) lie at the equilibrium.During the adsorption of NO 2 , CO 2 and SO 2 molecules over Pt-WSe 2 composite, gases will withdraw electrons due to their oxidizing nature.As it is also verified from the CDD, Mulliken, and Hirshfeld analysis as discussed in the aforementioned subsections.Upon NO 2 , CO 2 , and SO 2 adsorption, there is a depletion of electrons over Pt due to which it possesses a positive value and accumulation of electrons over target gas molecule (NO 2 , CO 2 , and SO 2 ) resulting in a negative value.Consequently, there is a depletion of charge carriers due to which the sensing material resistance gets modified.But, the H 2 molecule has a reducing nature due to which it donates electrons to the sensing layer.This is also confirmed by the CDD, Mulliken, and Hirshfeld analysis.Upon H 2 adsorption, there is the accumulation of electrons over Pt due to which it possesses a negative value, and depletion of electrons over H 2 resulting in a positive value.As it can also be observed that there is elongation in the H-H bond after adsorption over Pt-WSe 2 which confirms the spillover effect.As a result of this phenomenon, the H atom undergoes dissociation, leading to interactions with the WSe 2 layer, ultimately resulting in an increase in sensitivity to H 2 molecules.Furthermore, our computational results as mentioned in Table 5 affirm that the T V-WSe2 configuration exhibits higher sensitivity in the presence of H 2 gas molecules.Moreover, we examine the ϕ(s) of pristine and Pt-decorated where A, k B , and T represent attempted frequency (~ 10 -12 s −1 ) 42 , Boltzmann constant, and temperature, respectively.E a denotes the potential barrier for desorption which is equivalent to adsorption energy.As it can be seen the recovery time for the T V-WSe2 -based system to detect SO 2 is maximum at low temperatures due to strong adsorption energy.Moreover, due to strong adsorption energy among all configurations, the adsorption and desorption are dependent on activation and deactivation energy, respectively.The deactivation energy depends on temperature hence the recovery time decreases with an increase in temperature.As it can be depicted in Table S1 all three proposed configurations have faster recovery time in the case of H 2 gas molecules.In previous studies, it has been shown that the Pt loaded over 2D nanomaterial configuration is highly selective for the H 2 gas molecule.And among these systems adsorption energy is comparatively stronger in the case of T V-WSe2 -based H 2 gas molecule as aforementioned in the result and discussion section.Upon H 2 adsorption, there is an addition of energy states in the bandgap due to charge transport characteristics resulting in variation in the bandgap.

Conclusions
In this work, we have decorated Pt over the basal and vertical edge of WSe 2 and performed the DFT study for the gas sensing towards distinct target gases (H 2 , NO 2 , CO 2 , and SO 2 ) using the Dmol 3 package in Material Studio software.We have analyzed the electronic characteristics (bandstructure, DOS, CDD, and population analysis) of Pt decorated over the WSe 2 system with and without adsorption of target gases.We have analyzed recovery times for distinct combinations in which the H 2 adsorbed system shows quicker recovery in contrast to others.The rates of adsorption and desorption are directly influenced by the respective activation and deactivation energies, which exhibit a strong dependence on temperature.Moreover, the introduction of Pt onto WSe 2 induces a spillover effect, substantiated by the elongation of the target gas molecule.In the T V-WSe2 configuration, there is an increased presence of W edge sites, serving as additional adsorption sites for the gas molecule.Significantly, these W edge sites exhibit higher binding capacity and larger surface area contributing to an enhanced sensitivity in T V-WSe2 towards the target gas molecules.T V-WSe2 shows an excellent sensitivity for the H 2 molecule.The adsorption of gas molecules onto the sensing material causes a modulation in electrical conductivity, arising from the interaction between the adsorbed gas molecule and the sensing layer.Our work shows that the decoration of Pt over the vertically oriented WSe 2 enhances the sensing performance significantly.

Figure 1 .
Figure 1.(a) Top surface, and (b) side profile, of the 3 × 3 WSe 2 monolayer.(c) The electronic band, and (d) the projected density of states (PDOS) structure of the system is presented, herein the horizontal and vertical dashed line signifies the Fermi level in the band structure and PDOS, respectively.

Figure 2 .
Figure 2. Three possible configurations for decorating a WSe 2 monolayer with platinum atom: (a) at the hollow hexagonal site of the WSe 2 basal plane (T BH-WSe2 ), (b) atop a W atom within the basal plane (T BM-WSe2 ), and (c) at the vertical edge of the WSe 2 monolayer (T V-WSe2 ).

Figure 3 .
Figure 3.Most stable configuration and corresponding charge density distribution (CDD) following H 2 adsorption at three different sites where a Pt is decorated: (a) the hollow site in the basal configuration, (b) above the W atom in the basal configuration, and (c) along the vertical edge of WSe 2 .In the CDD diagram, electron depletion manifests itself in a rosy colour, while electron accumulation is represented by a green colour.

Figure 4 .
Figure 4. Optimal arrangement and associated charge density distribution after NO 2 adsorption at three distinct locations where a Pt is functionalized: (a) the hollow site in the basal configuration, (b) positioned above the W atom in the basal configuration, and (c) situated along the vertical edge of WSe 2 .Electron depletion and accumulation are visualized through the application of rosy and green colours.

Figure 5 .
Figure 5.Most stable configuration and corresponding charge density distribution following CO 2 adsorption at three different sites where a Pt is decorated: (a) the hollow site in the basal configuration, (b) above the W atom in the basal configuration, and (c) along the vertical edge of WSe 2 .Electron depletion and electron accumulation are mapped onto rosy and green colour regions, respectively.

Figure 6 .
Figure 6.Optimal arrangement and associated charge density distribution after SO 2 adsorption at three distinct locations where a Pt is functionalized: (a) the hollow site in the basal configuration, (b) positioned above the W atom in the basal configuration, and (c) situated along the vertical edge of WSe 2 .Electron depletion and accumulation are represented by the colour spectrum, with rosy signifying depletion and green signifying accumulation.

Table 1 .
Summary of electron distribution and H 2 gas adsorption distance in three proposed configurations.

Table 2 .
Summarizing electron distribution and adsorption distances post-NO 2 gas adsorption across three distinct proposed configurations.

Table 3 .
CO 2 adsorption behaviour is presented through electron distribution and distance analysis in three configurations.

Table 4 .
Provides a tabulated overview of electron distribution and SO 2 adsorption values for three distinct configurations.

Table 5 .
Summarizes the sensitivity of the three configurations to the target gas molecule.